1. Field of the Invention
The present invention relates to an intermittent coating apparatus for intermittently coating a continuously running base member with a coating material.
2. Description of the Related Art
An apparatus for intermittently coating a base member (i.e. an external coating target), which is continuously running, with a coating material such as an adhesive or a paint is known and described in, for example, Japanese Laid-Open Patent Publication No. 62-266157.
Briefly referring to FIG. 11, a typical structure of a conventional intermittent coating apparatus 800 will be described. FIG. 11 is a cross sectional view of the intermittent coating apparatus 800.
By the intermittent coating apparatus 800, a coating material is discharged through a slit 27 formed at a tip of a nozzle 26 and is applied to a continuously running base member 32. The intermittent coating operation is controlled in the following manner by the movement of a shaft 30 directly connected to an air cylinder 22. The movement of the shaft 30 in the direction of arrow B or the opposite direction is controlled by the flow of the air supplied through an air supply pipe 28.
In order to coat the base member 32 with the coating material, the shaft 30 is retracted in the direction opposite to arrow B. The coating material which is sent to a supply chamber 24 through a pipe 29 by a liquid supply device such as a pump is further sent to the slit 27 through a supply opening 31, and then is discharged through the slit 27 to be applied to the base member 32. In order to stop the coating operation, the air cylinder 22 is driven to move the shaft 30 in the direction of arrow B in order to cover the supply opening 31 with a head 25, thereby stopping the supply of the coating material to the slit 27. By driving the air cylinder 22 so as to alternately open and close the supply opening 31 in repetition, the base member 32 is coated with the coating material intermittently.
The intermittent coating apparatus 800 having the above-described structure is generally used to put the coating material on the base member 32 in a small amount such as several tens of cubic centimeters per square meter, or less. In the case that the intermittent coating apparatus 800 is used to coat the base member 32 with the coating material in a relatively large amount such as 100 cc/m.sup.2 or more, the leading edge and the trailing edge of areas of the base member 32 coated with the coating material are likely not to be clear, straight lines.
Such areas are schematically illustrated in FIG. 12. In FIG. 12, the base member 32 is running in the direction of arrow C. Reference numeral 20 denotes areas coated with the coating material on the base member 32 (referred to as coated areas hereinafter). As is illustrated in FIG. 12, a trailing edge 19 of each of the coated areas 20 is not a clear, straight line. Accordingly, a leading edge 21 of the respective following coated areas 20 is not a clear, straight line, either. Such a phenomenon occurs because the coating material existing between the nozzle 26 and the base member 32 or in the slit 27 of the nozzle 26 is unnecessarily pulled out onto the base member 32.
Especially in the case that the coating material in use tends to rope, the coating material in the slit 27 is easily pulled out by the running movement of the base member 32 even after the supply of the coating material to the slit 27 is stopped.
Further, in the intermittent coating apparatus 800, the shaft 30 for connecting the head 25 and the air cylinder 22 is supported only by a bearing portion 23. Due to such a structure, in the case that the forming precision of the shaft 30 and/or the bearing portion 23 is not sufficiently precise to properly align the head 25 and the supply opening 31, the supply opening 31 cannot be completely covered with the head 25. In such a case, the coating material possibly goes into the slit 27 through a slight gap around the supply opening 31 incompletely covered with the head 25, even after the shaft 30 is moved to such a position as to cover the supply opening 31 with the head 25. This also spoils the linearity of the leading edge 21 and the trailing edge 19 of the coated areas 20.